I do all my shopping at Nissen with one exception: the 2nd floor at National Azabu. This floor offers the best selection of new(not used), English literature anywhere in Tokyo. It also offers an array of greeting cards, cooking books, and kitchenware. The first floor not only offers processed goods: they have a fresh fish deli, a meat deli, and wonderful, French gourmet cheeses. However, it is just too small to shop comfortably not to mention the tourists who frequent this store to window shop (Japanese people from the surrounding Tokyo areas).
Delicious sweets and cheeses but at a hefty price. Don't miss out on the delicious macaroons made by la mama...heavenly, melt-in-your-mouth, treats.
The quiche and pastas are satisfactory when you want to take a rest from cooking...almost as good as home-cooking but not quite there.
I have been going to this supermarket for over 8 years. It has the largest selection of import food and liquor in Tokyo. Overall, the staff are friendly as well. Unlike National Azabu in Hiro-o, you don't have to fight crowds in a small space to do your weekly 'big shop' because the place is huge.